title: Arkadia represses the expression of myoblast differentiation markers through degradation of Ski and the Ski-bound Smad complex in C2C12 myoblasts.
abstract: The differentiation of myoblasts is regulated by multiple extracellular and intracellular factors. Of the extracellular regulators, members of transforming growth factor-beta (TGF-beta) family play critical roles in the regulation of osteoblasts and myoblast differentiation. Little is known, however, about the regulation of Myostatin/TGF-beta signaling during myoblast differentiation. In this study, we examined the roles of Arkadia, an E3 ubiquitin ligase, in Myostatin/TGF-beta signaling and the regulation of myoblast differentiation. Knockdown of Arkadia reduced Myostatin/TGF-beta signaling and enhanced the differentiation of C2C12 myoblasts. In addition, exogenous overexpression of Arkadia enhanced Myostatin/TGF-beta signaling, preventing myoblast differentiation. In the absence of the activation of Myostatin/TGF-beta signaling, knockdown of Arkadia enhanced myoblast differentiation via upregulation of Ski protein, an intracellular enhancer of myoblast differentiation. Arkadia likely affected the differentiation of myoblasts in a Smad-independent fashion by inducing Ski degradation. Knockdown of Arkadia increased the Myostatin-induced phosphorylation of Smad2/3 in C2C12 cells. Arkadia bound Smad2/3 via Ski to induce the ubiquitination of Smad2/3. These results suggest that Arkadia targets Ski-bound, inactive phospho-Smad2/3 to regulate positively Myostatin/TGF-beta signaling. Taken together, this study indicates that Arkadia regulates myoblast differentiation through both Smad-dependent and Smad-independent pathways.
authors.affiliation: Division of Biochemistry, The Cancer Institute of the Japanese Foundation for Cancer Research (JFCR), Ariake, Tokyo, Japan.
authors.forename: Hisanori
authors.initials: H
authors.lastname: Yuzawa
authors.forename: Daizo
authors.initials: D
authors.lastname: Koinuma
authors.forename: Shingo
authors.initials: S
authors.lastname: Maeda
authors.forename: Kengo
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Keiji
authors.initials: K
authors.lastname: Miyazawa
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imamura
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D046912:Multiprotein Complexes / Q000378:metabolism; D032446:Myoblasts / Q000166:cytology* / Q000378:metabolism*; D055435:Myostatin / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D015398:Signal Transduction; D051785:Smad Proteins / Q000378:metabolism*; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases; D054875:Ubiquitination
chemical_list: D015415:Biomarkers; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; D055435:Myostatin; D011518:Proto-Oncogene Proteins; C512653:Ski protein, mouse; D051785:Smad Proteins; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D016212:Transforming Growth Factor beta; D025801:Ubiquitin; C427283:Rnf111 protein, mouse; D044767:Ubiquitin-Protein Ligases